1. Field of the Invention
The present invention relates to a refrigerant cycle including an ejector. The refrigerant cycle is provided with a bypass passage through which a part of high-pressure refrigerant from a radiator bypasses a nozzle of the ejector, and a control valve that opens the bypass passage when the pressure of the high-pressure refrigerant is higher than a valve-opening pressure of the control valve.
2. Description of Related Art
In a refrigerant cycle (ejector cycle) described in JP-A-6-2964, refrigerant is decompressed and expanded in a nozzle of an ejector so that gas refrigerant evaporated in an evaporator is sucked, and pressure of refrigerant to be sucked into a compressor is increased by converting expansion energy to pressure energy. For example, a conventional refrigerant cycle shown in FIG. 13 includes a compressor 101 for compressing refrigerant, a radiator 102 for cooling high-pressure refrigerant discharged from the compressor 101, an ejector 103, a gas-liquid separator 104, a flow control valve 105 and an evaporator 106. Further, the ejector 103 is constructed with a nozzle 131, a suction port 132, a mixing portion 33 and a diffuser 134. The nozzle 131 decompresses the high-pressure refrigerant introduced from the radiator 102 to a high-pressure refrigerant inlet 131a, so that low-pressure refrigerant evaporated in the evaporator 106 is sucked from the suction port 132 into the mixing portion 133 by a high-speed refrigerant stream jetted from an outlet 131c of the nozzle 131. The sucked refrigerant from the evaporator 106 and the jetted refrigerant from the nozzle 131 are mixed in the mixing portion 133. Further, the mixing portion 133 and the diffuser 134 increase the refrigerant pressure by converting the speed energy of refrigerant to the pressure energy of refrigerant. Thereafter, refrigerant flows into the gas-liquid separator 104 from an ejector outlet 135.
In the ejector cycle, because a sectional area of a throat portion 131b of the nozzle 131 is fixed, a flow amount of refrigerant flowing into the nozzle 131 of the ejector 103 cannot be adjusted based on operation condition (e.g., cooling load) of the refrigerant cycle. When the refrigerant cycle is used for a vehicle air conditioner, the compressor 101 is generally driven by a vehicle engine, and a rotational speed of the compressor 101 is largely changed due to a rotation speed of the vehicle engine. Accordingly, the refrigerant pressure may be excessively increased, and the efficiency of the refrigerant cycle may be greatly deteriorated. Further, when carbon dioxide is used as the refrigerant, the pressure of high-pressure refrigerant is greatly changed, so it is difficult to stably operate the refrigerant cycle.